Light-duty combustion engines may be used in hand-held tools and other pieces of equipment that have rotating, reciprocating, or otherwise moving parts. In order to prevent these tools from engaging immediately upon startup, they may be equipped with centrifugal clutches that only engage once the engine speed exceeds a predetermined clutch-in speed.
For example, consider the case of a gas-powered weed trimmer having a rotating trim line that can be used to cut grass, weeds, plants, etc. The weed trimmer can be equipped with a centrifugal clutch that prevents rotation of the trim line when the engine is operating below a certain speed. This way, when an operator initially starts the engine—a period when the operator may not be fully prepared for the tool to start rotating—the engine can warm up without the trim line rotating. Once the operator is ready for normal operation, the engine can be brought up to a speed that is sufficient to engage the centrifugal clutch and begin spinning the trim line.